Inclusion Criteria:

• Meets Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM IV) criteria for Bipolar I Disorder, Most Recent Episode Manic or Mixed (with or without psychotic features)
• History of at least 1 previously documented manic or mixed episode requiring medical treatment within 3 years before the screening phase
• Total score of at least 20 on the YMRS at screening and at baseline
• If taking mood stabilizers, antipsychotics, or antimanic drugs, must have discontinued that medication at least 3 days before baseline
• Women must be postmenopausal (no spontaneous menses for at least 2 years), surgically sterile, abstinent, or agree to practice an effective method of birth control if they are sexually active before entry and throughout the study (effective methods of birth control include prescription hormonal contraceptives, intrauterine devices, double-barrier method, and male partner sterilization)
• Able and willing to comply with self-administration of medication, or have consistent help or support available

Exclusion Criteria:

• Meets DSM-IV criteria for rapid cycling and schizoaffective disorder
• In the opinion of the study doctor, is at significant risk for suicidal or violent behavior during the course of the study
• Has used cocaine, phencyclidine, amphetamine, methylphenidate, pemoline, an opioid (excluding codeine), hallucinogen, or any other drug that may be associated with manic symptoms as evidenced by a positive urine drug screen
• Has received benzodiazepines at doses equal to 4 mg/day of lorazepam or higher for a period of 3 months or longer immediately before the screening phase.